1. Field
A technique to control a direction of light emitted from a light guide plate is disclosed.
2. Description of the Related Art
A liquid crystal display (LCD) displays an image by transmitting or blocking light emitted from a planar light apparatus such as a backlight and the like using a polarizer and liquid crystal.
The polarizer used in the liquid crystal display (LCD) is generally manufactured by using a polyvinyl alcohol (PVA) film colored with iodine and stretched in one axis direction, and attaching a triacetyl cellulose (TAC) film as a protection film to one side or both sides of the polyvinyl alcohol (PVA) film. In addition, the TAC film may be replaced with an absorption-type polarizer manufactured by disposing a coating layer such as an acrylic resin and the like on one side of a polarizer or attaching a phase difference film such as norbornene, polycarbonate, or the like thereto.
However, this absorption-type polarizer has a characteristic of transmitting light in its transmission axis direction but absorbing the other light components, and thus may not theoretically exceed light utilization efficiency of about 50% and may just reach a maximum of about 48% considering a reflection rate on the internal surface thereof of 4%. Accordingly, effective utilization of light emitted from the backlight and the consequent luminance improvement of the backlight are desirable of the liquid crystal display (LCD). These may be obtained by using a reflective polarizer having optical reflection interference characteristics.
The reflective polarizer reflects light of a particular polarization but transmits light of the opposite polarization and is used as follows.
The reflective polarizer is disposed in the same axis as the absorption-type polarizer, so that the light transmitting from the reflective polarizer may pass through the absorption-type polarizer in linear polarization.
Accordingly, the absorption-type polarizer may improve the utilization efficiency of light emitted from the backlight by reflecting polarized light absorbed in the absorption-type polarizer with the reflective polarizer and then turning the polarized light back to the backlight and reusing the polarized light.
The reflective polarizer may be a brightness enhancement film, for example, DBEF (registered trademark) made by Sumitomo 3M Ltd. This brightness enhancement film is formed of hundreds of stacked polymer films by controlling a precise process to secure polarization characteristics over a wide visible light region as a result of which it is expensive.
Accordingly, Japanese Patent Laid-open No. 11-502036 discloses a reflective polarizer using a polarization sensitive scattering element (PSSE) as a method of decreasing the manufacturing cost. Japanese Patent Laid-open No. 11-502036 realizes polarization separation by transmitting light of one particular polarization while at the same time scattering light of other polarizations. The reflective polarizer detailed by Japanese Patent Laid-open No. 11-502036 does not display sufficient polarization separation efficiency and in addition does not display much high light utilization efficiency, since undesirable polarized light is scattered and transmitted forward.
In addition, Japanese Patent Laid-open No. 2006-517720 realizes polarization separation by using a fiber having birefringence as the polarization sensitive scattering element (PSSE) and integrating the fiber with a light guide plate having an isotropic refractive index. Japanese Patent Laid-open No. 2006-517720 realizes polarization separation by scattering light of one particular polarization in a layer formed of the fiber that displays birefringence. The polarized light is emitted externally. In addition, Japanese Patent Laid-open No. 2006-517720 barely increases utilization efficiency of light, since a part of the scattered light and the other polarized light (in the layer formed of the fiber having birefringence and the matrix) is emitted through the light guide plate (LGP) and subsequently becomes extinct. In addition, the direction of the scattered and emitted light is reported to be determined by the shape of the fiber, but since externally emitted light is actually divided into two directions, the emitted polarized light may not be efficiently used.